1. Field of the Invention
This invention relates to the drying and burning of waste materials such as sewage sludge.
2. State of the Art
Conventional wastewater treatment processes remove pollutants from the wastewater and generate slurries of the removed pollutants. These slurries are generally known as sludge, which contains organic materials as well as a high percentage of water. Disposal of the sludge is accomplished by known methods, and one such method includes dewatering the sludge by filtration and incineration of the dewatered sludge.
It is generally recognized that filtration of sludge removes only a fraction of the water, and substantial quantities of water remain with the sludge even after filtration. Therefore, it is desirable to remove additional water from the sludge prior to incineration so that it is not necessary to heat substantial quantities of water in the incineration step.
One conventional process for removing additional water from filtered sludge includes heating the sludge prior to incineration. In a dryer, the sludge is contacted with hot combustion gases from the incineration step so that the sludge is heated and water is driven off as vapor. When the sludge is heated, malodorous gases as well as water evolve from the drying sludge and they are carried from the dryer by the combustion gases. These gases are then passed through a condensor wherein the water vapor condenses and is disposed of, and the dry, malodorous gas is returned to the incinerator to be burned.
It should be appreciated that a gas has a relatively low heat capacity, and therefore large quantities of the combustion gas must be contacted with the sludge in order to effectively heat and dry it. Moreover, a large dryer and condenser are also necessary to handle the large volumes of gas.